Top: HST/STIS G140M spectral image of IRAS 0833. Spatial extension is ~ 19″ (~7.5 kpc) . Middle: emission profile of the main component of Lyα (blue) and UV continuum (1224.5 Å rest frame, black) from STIS data, and Hα (dashed red) from ACS data. Bottom: spatial profiles of Lyα (blue) and observed Lyα/Hα (solid black) and Hα/Hβ (from WHT/ISIS data, in red), and the expected Lyα/Hα ratio (dashed brown), assuming Case B recombination and internal reddening as derived from the Hα/Hβ ratio, as well as the Galactic extinction. The Lyα escape fraction , as defined in the text, has been plotted in dotted black line. In the middle and bottom panels, the negative x-axis corresponds to north, as indicated by N. To ease the comparison, the dashed red line in the middle panel shows the Hα profile scaled by a factor 0.2. The vertical scale corresponds to the Lyα and non-scaled Hα fluxes. Whereas the vertical scale of the left axis in the bottom panel corresponds to the Lyα/Hα and Hα/Hβ ratios, the scale of the right axis corresponds to . Position of the region LyαS is marked.